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In Reply to: RE: Interstage transformer to 600R recommendation needed posted by Joshua_G on December 05, 2013 at 14:57:50
The LL1671 is probably the best choice for this tube. You can use it 2:1 or 4:1. Getting an LL1671 gapped for 50mA or 60mA is no problem.
I have found that terminating a line out or interstage transformer with a resistor that results in a reflected impedance approximating the plate impedance, or even perhaps 5x higher really decreases my fondness for the sound of music played through it. I started out many years ago thinking that loading was a good thing because it flattened the ever-present high frequency resonances above 30KHz. However, when I actually listened, the line stage took on a lazy sound lacking in space and dynamic contrasts. If resonances are an issue, it is better to attack them with an RC network that is frequency selective. It doesn't seem to damage the sound.
Kevin Carter
K&K Audio
www.kandkaudio.com
Follow Ups:
Hi Kevin,
Thank you.
I’m considering options aloud…
With E55L in triode mode have mu of 50, thus 4:1 turns ratio seems a reasonable option to tame the gain of that stage, since even 22dB gain for a preamp is on the high side.
The plate impedance of the E55L in triode mode is 600R. My power amp input impedance is 20K. The reflected impedance as load to the tube will be 320K. Is there no problem with it?
What will be the primary inductance of the LL1671/60mA?
Can its’ low frequency roll off be estimated under the conditions I described (tube’s ri 600R, load 20k)?
In reality, the tube performs the best with a negligible load, which is why constant current source loads sound better than resistive loads.
The primary inductance with the C side windings in series with a 60mA gap would be about 18H. The roll-off can be estimated using the equations in the LL1620 data sheet.
Kevin Carter
K&K Audio
www.kandkaudio.com
Hi Kevin,
Thank you.
I got my answers.
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